Abstract

Photodissociation mechanisms of nitrosamine have been studied at the complete active space self-consistent field level of theory in conjunction with atomic-natural-orbital-type basis sets. In addition, the energies of all the critical points and the potential energy curves connecting them have been recomputed with the multiconfigurational second-order perturbation method. Ground state minimum of nitrosamine has a nonplanar structure with the hydrogen atoms of the amino moiety out of the plane defined by the N–N–O bonds. Electronic transitions to the three lowest states are allowed by selection rules: (i) has an oscillator strength of and it is assigned as an transition, (ii) has an oscillator strength of and it is assigned as an transition, and (iii) has an oscillator strength of and it is assigned as an transition. It is found that N–N bond cleavage is the most likely process in all the photochemical relevant states, namely, , , and . While and yield exclusively homolytic dissociation: , on the latter process constitutes the major path, but two additional minor channels are also available: adiabatic homolytic dissociation: , and adiabatic oxygen extrusion: . The excited species experiences a subsequent ultrafast decay to the ground state, the final products in all cases the fragments being in their lowest electronic state. We have not found a unimolecular mechanism connecting excited states with the ground state. In addition, homolytic dissociation in the ground state, tautomerizations to NHNOH and NHNHO, and intersystem crossings to are considered. The most favorable process on this state is the isomerization to NHNOH.

Received 01 August 2006Accepted 12 September 2006Published online 24 October 2006

Acknowledgments:

This research has been supported by the Spanish Ministerio de Educación y Ciencia (Project No. BQU2003-1426). One of the authors (D.P.) thanks the Spanish Ministerio de Educación y Ciencia for Grant No. BES-2004-6033. The authors thank Professor Dr. J. Márquez and Dr. F. J. Alonso from the Biochemistry Department for fruitful discussions on the biochemistry of nitrosamines.

Article outline:I. INTRODUCTIONII. METHODS OF CALCULATIONIII. RESULTS AND DISCUSSIONA. Vertical transitionsB. Photodissociation of nitrosamine into and NO on the lowest-lying valence singlet surfacesC. Homolytic dissociation of nitrosamine on ground state and tautomerizations to hydroxydiimide (NHNOH) and diimide-N-oxide (NHNHO)D. Triplet state surfacesIV. SUMMARY